Method and apparatus for honing



July 9, 1945. J. o. OLSEN 2,403,546

I METHOD AND APPARATUS FOR HONING Filed sept. 27, 1943 s She ets-Sheet 1- ENVENTOM 3 Sheets-Sheet 2 J. O. OLSEN METHOD AND APPARATUS FOR HONING Filed Sept. 27, 1943 July 9, 1946.

7 I 3 I 5 4 A. 5 5 f 5 8 B W a 2 O My 0 Mu A m +1. m w l 4 y 9, 1946. J. o. OLSEN METHOD AND APPARATUS FOR HONII G 3 Sheets-Sheet 3 Filed Sept. 27, 1943 5 i m w v as z x x IYQ w o mmnwmmmi mm oln Patented July 9, 1946 METHOD AND APPARATUS FOR HONING Joseph 0. Olsen, Rockford, Ill., assignor to Barnes Drill 00., Rockford, 111., a corporation of Illinois Application September 27, 1943, Serial No. 563,886

11 Claims.

The invention relates to the art of finishing cylindrical surfaces and more particularly to the honing art.

The honing process, in which a cylindrical abrasive tool and the work are relatively rotated and simultaneously relatively reciprocated axially, is employed extensively in finishing cylindrical surfaces Where a smooth, true surface and a high degree of accuracy is required. This process is capable of finishing either internal or external cylindrical surfaces to precise dimensions, accuracy within limits as close as plus or minus .0001 inch being readily attainable. In order to maintain such accuracy it has been necessary heretofore to interrupt the operation frequently for gauging the size of the work, particularly as the desired final dimensions are approached. Such interruption substantially increases the finishing time required and consequently reduces the productive capacity of the machine upon which the honing operation is performed. Moreover, a high degree of skill is required to gauge the work within the close limits referred to and the gauging is especially difficult when the internal surface of cylindrical bores are involved. These considerations all contribute to increasing the cost of the finishing operation. 7

With the foregoing in view a general object of the invention is to provide an improved method of and apparatus for gauging work in process of being honed whereby the size thereof may be determined with a high degree of precision at any stage of the honing operation and without interrupting the operation whereby the machine time and labor required for finishing a workpiece is reduced to a minimum with a consequent reduction in the cost of the operation.

Another object is to provide novel means operative to automatically gauge the work and provide a continuous indication of the size thereof while the honing operation is in progress.

Still another object is to provide novel means whereby a cylindrical bore may be quickly and accurately gauged for size throughout its entire length.

It is also an object of the invention to provide an improved honing tool having novel work gauging means, incorporated directly therein.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings in which:

Figure 1 is a fragmentary side view of' a honing machine and tool embodying the features of the invention.

Figs. 2, 3 and 4 are side views of the honing tool shown in difierent sections of a cylinder bore in process of being honed.

Fig. 5 is a vertical sectional view of the fluid distributing head associated with the tool.

Fig. 6 is a sectional View taken in a horizontal plane substantially on the line 6-6 of Fig. 5.

Fig. 7 is a side elevational view of the honing tool showing the location of the gauging mechanism associated therewith.

Fig. 8 is a sectional view taken in a vertical plane substantially on the line 88 of Fig. 7.

Figs. 9 and 10 are sectional views taken in horizontal planes substantially on the lines 9-9 and |0-I0 of Fig. 8, respectively.

Fig. 11 is a horizontal sectional view of a modified form of nozzle adjusting mechanism.

Fig. 12 is a sectional view taken in a vertical plane substantially on the line l2-I2 of Fig. 10.

Fig. 13 is a graph showing the relationship between the spacing of the coolant discharge orifices from the surface being honed and the pressure of the liquid coolant discharged through such orifices.

The improved gauging method may be carried out with. various types of honing machines and tools for finishing either internal or external cylindrical surfaces. For purposes of illustration theapparatus for carrying out the method has been shown herein as constructed and arranged for the honing of internal cylindrical surfaces such as cylinder bores. The particular machine selected to exemplify the honing operation is of the type in which the honing tool is rotated and simultaneously reciprocated relative to a stationarily supported workpiece. It is to be understood, however, that the invention is not limited to use in the particular environment shown but is readily applicable to other types of machines and honing tools. The invention accordingly, embraces all modifications, adaptations and alternative constructions falling within the scope of the appended claims.

' Referring to Fig; 1 of the drawings, a typical machine for honing cylinder bores comprises a head l5 adapted to bereciprocated by a pressure fluid operated actuator I6 of the cylinder and piston type. J ournaled in the head and projecting from one face thereof is a spindle l! to which a honing tool I8 is operatively secured by means of an elongated tubular driver Hi. The spindle I1, driver l9 and tool l8 are rotatably driven by a motor M through suitable gearing.

The honing tool l8 may be of any preferred type. Such tools ordinarily include a generally cylindrical body 2i (Figs. 1, 7, 8 and 12) having a plurality of radially movable elongated abrasive stones 22 assembled thereon in a circular series. The abrasive stones are conveniently mounted in elongated carriers 23 (Figs 8 and 12) which provide rigid support 'for'the' stones and guide the same for radial movement in the tool body 2|. Annular springs '26 encircling the series of carriers yieldably urge the carriers and abrasive stones inwardly to a contracted position.

In operation, the tool is expanded, that is, the carriers 23 and abrasive stones 22 are shifted radially outwardly to force the working faces of the stones against the surface to be finished. In the exemplary tool, the means for-effecting such expansion comprises a pair of generally conical cam members 25a'nd 25' slidaole but nonrotatably held within the hollow to'ollbody 2! for coaction with adjusting plates 26 (Fig, 12) associ'ate'd' with the respective carriers 23. The cam members are mounted in oppositely'facing" relation upon a shaft 21, the member 25 being rotatably anchored to one end of the" shaft while the member 25' is threaded on the other end' of the shaft. J

By'turning the shaft 27 in one direction, the cam' members 25 and 25' are moved toward each other and act through the plates 26 to shift the carriers 23 and their abrasive stones 22 radially outwardly. A spring 28' interposed between the cam members yieldably urges themembers away from each other when the shaft is turned in the opposite direction thus permitting the springs 24 to shift the carriers and abrasive'stones' radially inwardly and thus contract thetool.

The shaft 2111s adapted to be turned by an adjusting rod 2.8 connected to the" upper end of the shaft by a flexible joint 29. The rod extends axially through the driver to a point at which it may be conveniently operated by an adjusting sleeve 30 (Fig. 1).

In honing a cylindrical bore such as the bore 33 of a metal block or workpiece W' thetool i8 is" inserted therei'nin a collapsed condition, that is; with the abrasive stones 22 withdrawn inw my sothat the overall diameter of the tool is'les's" than the diameter of the bore. After insertion the tool is expanded until the working facesof the stones 22 are pressed against the walls of the'bore. The stones are therefore effective to abrade or cut away the walls of the bore when th't'ooli's rotated and reciprocated therein. As'th'e here is gradually enlarged by the action of the abr'asivestones' 22; the tool is progressively expanded to maintain the required working pressure ori the work. Throughout the entire operation the work and tool are flooded with a copious supply of liquid coolant which serves to fiush away metal and abrasivechips and to prevent the tool and work from becoming overheated.

In finishing cylindrical workwithin the close limits demanded in precision honing, the honing operation must be terminated at the precise instantthat the desired finished diameter is attained. This dimension can be determined with the required accuracy only'by'the actual gauging ormeasurement of the work. Numerous attempts have been made to develop automatic work gaug ing means with a view of reducing the labor required and avoiding the delays involved in manualg'auging as now generally practised.

The useof automatic mechanism for inserting 4 plug gauges in the work in alternate strokes of the tool has been proposed, but has proven incapable of operating with the degree of precision required. Moreover, in apparatus of that type, the gauges are subject to excessive wear and, at best, are adapted only for gauging the extreme endsof the workpiece. Such apparatus, therefore, does not'disclose irregularities intermediate the ends of the work. The use of leakage path air gauges has been suggested to overcome the latter difiiculty. Air gauges have been found unsatisfactory however, due to the necessity of maintaining the tool and work flooded with liquid coolant.

I have discovered that the above difficulties may be completely avoided by employing the liquid coolant as the gauging medium and have provided the novel gauging method and apparatus herein disclosed for utilizing that discovery. The improved method of gauging contemplates the discharge of the liquid coolant under pres sure through one or more restricted outlets defined jointly by the work surface and members 40 carried by or movable with the honing tool whereby the flow of liquid is restricted in accordance with the diameter of the work. Variations in diameter may therefore be determined with a high degree of accuracy by measuring changes in either the volume or the pressure of the liquid in the coolant system. In practice, I pre-- fer' to supply a constant volume of the liquid coolant to the tool and to determine size by measuring the pressure in the coolant supply system.

The members 40 coacting with the work sur-' face to define the coolant outlets are preferably mounted directly on the tool body. These members, while adjustable relative to the tool, are held in fixed spaced relation during the honing operation. The spacing may be adjusted initially to provide a predetermined gap or outlet between each member and the unfinished work surface. Accordingly, the pressure in the coolant supply system is at its maximum when the tool is initially associated with the work, as for example, when it is inserted in a bore of small diameter. As the bore is progressively enlarged due to the gradual removal of stock bythe tool, the gaps between the work surface and the members 40 increase and the pressure drops corre-' spondingly. Thus, as the honing operation proceeds, the pressure gradually falls in accordance with the progressively increasing diameter of the bore. It will be evident therefore, that'the pressure of the liquid coolant provides an accurate indication of the diameter of the work at the particular pointat which the tool is positioned.

To establish a definite reference point for the accurate gauging of the work, the members 48 are preliminarily set by means ofa ring gauge 4| (Fig. 1) or the like having an internal diameter corresponding exactly to the desired diameter of the finished work. With the members set-so that they may be inserted in an unfinished bore, the pressure set up by the gauge corresponds to the pressure that will obtain when thefwork is finished to the desired size. Accordingly, the honing operation may proceed without interruption until the pressure in the coolant supply system indicates that the desired dimension has been attained. Moreover, localized constricted areas or taper in the work are indicated by appropriate pressure changes in the coolant supply system thus enabling the machine attendant to amplify .the action of the tool in such areasby shortstroking.

. The apparatus for carrying out the improved gaugingmethod may take various forms. In the preferred embodiment illustrated the members 48 which, in cooperation with the work surface define the coolant outlets, comprise tubular nozzles .42 supported on the body of the honing tool and tends to center them in the work. Additional nozzles may be provided if desired to accommodate a greater volume of coolant.

In the exemplary apparatus, each of the nozzles 42 is fitted into and rigidly secured to a generally rectangular metal block 43 (Fig. 8) havin cylindrical mounting studs 44 and 45 projecting from its upper and lower faces. The upper stud 44 is formed with an axial bore or passage 46 communicating at its lower end with the nozzle. A coupling 41 threaded on the upper end of the stud connects the passage 46 with a flexible tube 48 which has its other end connected by a coupling 49 with a coolant distributor 50 carried on the driver [9.

Cooperating with the mounting studs 44 and 45 to support nozzles on the tool body are a pair of yokes 5| and 52. The yokes are of similar form, each comprising a metal plate having a central aperture dimensioned to fit loosely over the end of the tool body 2i and having laterally projecting arms apertured to receive the studs. The couplings 41 engage the upper face of the yoke 5| and act to clamp it rigidly against stop shoulders 53 formed on the studs 44. Nuts 54 threaded onv the lower ends of the studs 45 clamp the lower yoke 52 against stop fianges 55 formed on the studs. Thus the nozzles are supported by a rigid frame structure mounted for limited movement transversely of the tool body 2|.

Adjustment of the nozzles with respect to each other may be readily effected either by shifting the studs toward or from each other in the yokes.

Alternatively, the nozzles may be readily replaced by nozzles of different length or shape or having different size orifices.

To guide the nozzle supporting structure in its lateral movements, the tool body 2| is formed with radially opening recesses 56 adapted to snugly receive the inner ends of the nozzle supporting blocks 43 which have their side edges tapered as shown in Figs. 9, 10 and 11 to permit them to fit between the adjacent abrasive stone carriers. Detents 51, herein shown as spring pressed balls carried by the blocks 43, engage the walls of the recesses to prevent undesired movement of the nozzle supporting structure.

Means is provided for automatically effecting the adjustment of the nozzles and associated supporting structure to center the nozzles in a bore and maintain'this central position throughout the honing operation and thus compensate for uneven wear of the abrasive elements of the tool.

The means provided for this purpose comprises a pair of plungers 58 slidably fitted in recesses in the blocks 43 for movement radially of the tool body into engagement with the walls of the bore. Springs 58 acting on collars 60 integral with the plungers urge the latter outwardly against the the tips of the plungers so that in their limit positions contact between the plungers and the work surface is interrupted during the final stages of the honing operation. In this way any possibility of the plungers marking the finished surfaces is effectually avoided.

' vWhen the honing tool is used for removing small amounts of stock, a single coolant outlet may be used if desired. Moreover the automatic centering plungers may be replaced by fixed adjusting screws 62 adapted to thread into the stop plates BI and to bear against the tool body as shown in Fig. 11. Thus by appropriate manipulation of the screws 62, the nozzles 42 may be shifted toward or from the axis of the tool body and accurately centered with respect to the working faces of the abrasive stones.

As stated heretofore, the supply of liquid coolant is delivered to the nozzles 42 through the distributor 50 which acts to provide a connection between the rotating tool and a stationarily supported coolant source. As shown in Figs. 5 and 6, the distributor comprises a central body H in the form of a cylindrical enlargement of the driver I9. Vertical passages 12 in the body communicate at their lower ends with the tubes 48 leading to the nozzles 42. Each passage 12 is closed at its upper end by a plug 13 and it is provided with a radially opening port 14 formed by a circumferential groove in the body I l.

Rotatably mounted on the distributor body H is a sleeve 15 having an inlet opening 16 to which coolant is delivered through a pipe IT. The inlet is alined with the groove forming the ports 14 whereby coolant is delivered to passages 12 dur-v ing the rotation of the distributor body relative to th sleeve 15 which remains stationary. To prevent endwise movement of the sleeve relative to the distributor body, the sleeve is confined between a flange 18 projecting outwardly from the lower end of the body and a collar 19 clamped to the body.

Liquid coolant may be supplied .to the distributor 55 for delivery to the nozzles 42 from any suitable source capable of delivering a substantially constant volume of liquid under pressure. As shown in Fig. 1, the coolant source comprises a constant volume adjustable delivery vane pump P driven by an electric motor MI. The pump is adapted to draw liquid coolant through an intake line 19 from a settling tank or reservoir R and discharge it under pressure through a pipe to which the pipe 11 is connected as by a T-fitting 8|. A pressure gaug 82 is connected with the other outlet of the fitting 8| to visually indicate the pressure in the coolant supply system. Adjustment of the pump output is effected in well-known manner by means of a manually operable adjusting member 83.

Before the gauging apparatus is placed in operation the nozzles 42 are initially adjusted so that their outer ends are within but in close proximity to the cylindrical path described by the working faces of the abrasive elements 22 in the rotation of the tool. The nozzles are therefore separated by'a relatively small gap from the unfinished walls of the bore thus DIOVidiIlg a restricted outlet for the fiuid discharged from thenozzles. The output of the pump -P may then be adjusted to provide any desired pressure for the outlet thus formed, the pressure being indicated by the gauge 82. As stock is removed by the tool (increasing the diameter of the work in the case of an internal cylindrical surface and decreasing the diameter in the case an external cylindrical surface) the p cing-of the work: surfacefromithenozzlesincreases thus increasing: the area of the 'coolant outlet 'and-causing a pressure dropin the supply system-1.. Thispressuredropprovides an accurate indication of the change in the diameter of the work. v

For rough honing, where a substantial amount of stock is to-be removed, operation ofthe gauging-apparatus with outlets of substantial area, thatis, with relatively large gaps between-the nozzlesand the work surface and at relatively low pressure will ordinarily be found most satisfactory. For example, the nozzles maybe set to provide initial gap'of .015 inches between the outer end of each nozzle and the Work surface and the pump delivery adjusted'to produce a pressure in the system of approximately twenty pounds per square inch. With this setting, removalof' .OlQ inch of stock and the consequent enlargement of the gap at each nozzle to .020 inch Will result in a pressure drop of approximately ten pounds as indicated by the bracketed section X of thepressure curve shown in Fig. 13. In otherwords, under the conditions stated each pound variation in the pressure corresponds approximately to.00linch of stock measured on the diameter of the work.

For high precision finishing where relatively little-stockis removed, greater sensitivity is obtained with a smaller outlet; that is, when the nozzles are set'closer to thework'surface and the pump adjusted for operationiin the higher pressure range indicated by the bracket Y in Fig. 13. Thusa-with an initial gap of .007 inch between the outer end of eacnnozzle and the work surface and with the pump adjusted to produce a pressure of" seventy pounds per square inch in the coolant supply system, an increase of .002 inch in t'he spacing of the nozzles from the work surface-or an increase of .094 inch in the work diameter will result" in a pressure change of approximately twenty pounds per square inch. Accordingly, much more accurate gauging may be effected due to the relatively large pressure changes produced'by relatively small changes in work diameter.

It will be understood, of course, that with either type ofadjustment, the gauging apparatus is calibrated initially with reference to a suitable gauge. When used with an external honing tool, a conventional cylindrical plug gauge is utilized for this purpose. For apparatus used with an internal honing tool, the ring gaug 4! is utilized as previouslyexplained. The honing operation is started'with a substantially higher pressure than that produced by the. calibrating gauge and the operation is continued until thepressure indicated by the gauge 82' corresponds exactly with that produced by the calibrating gauge. It will also be understood that the gauging apparatus may be calibrated to indicate actual diameters, if desired;.

The gauging apparatus above described is adapted to accurately indicate any variations in the diameter of a bore at any point throughout its length. Thus when the tool is operating in a cylindrical bore having a slight taper developed in a preceding. operation, the pressure of the coolant is low when the tool is located in the large end'oi' the bore as shown in Fig. 2, a pressure of forty five pounds per square inch being indicated on the gauge 82 in this instance. As th tool is moved downwardlyv to the. smaller end of the bore the pressure. gradually risesto approximately sixty pounds as shown. in Fig; 3, thus indicating a substantial contraction of the here at that point. With these indications for guidance, tlielatt'end ant mayoperate the machine in well-known m'anner to short-stroke the tool within the constricted 'areauntil the diameter is substantially uniform-throughout the length of the bore. The t'o'ol may then be traversed axially of the bore in the usual wayuntil the honingxop'erati'on is completed. When the desiredfinal dimension-is attainedlthe gauge 82 registers a pressure of twenty-'pounds per square inch (Fig. 4'0- corresponding exactly with the indication given when thehone is associated with thec'a'librating gauge 41- as shown in Fig-1 thus enabling-the attendant to terminate the honing operations: cit the proper time.

It. will be apparent from the foregoing thatthe invention provides an improved method of gameingworkpieces in process of being'honed which permits? the Workto be finished precisely to-d'esired dimensionsW-ithout interrupting the honing operation. The time andlabor required for precision finishing of cylindrical work by honing is substantiall reduced thus increasing the productive capacity of the machine used for performing the honing operation and correspondingly reducing the cost of the finishing operation. Furthermore,v due to the constant visible gauging, oversize honing of the-workis avoided thus eliminating or substantially. reducing spoiled or scrapped work.

The. invention also-provides new and improved apparatus for carrying out the improved method of gau'ging; In particular, theapparatus is designed to utilize liquid coolant as the gauging medium, thereby adapting the fluid gauging meth'od for usein the honing process which requiresa constant how of liquid coolant over the tool and work. It should be understood, however, that the-gauging apparatus can be operated with liquidsother than the coolant ordinarily employed in honing provided such liquids do-not interfere with theproper functioning of the coolant. As a matter: of convenience, the gauging apparatus may be incorporated directly in" the tool.

The-improved apparatus is simple and rugged in construction and yet adapted to provide'extremely accurate measure ofth'e work size. When desired,' a continuous indication of size is available thus providing. for accurategauging of a bore or the like during the'entire operation. Moreover, a.cylindricalworkpiecemay be gauged accurately throughout its length with a minimumof effort on the part' of the operator and Without loss of time.

While the exemplary gauging method and apparatuscont'emplates the discharge of a constant volume of liquid coolant. through the gauging out'letswith: measurement of pressure variations, it will be appreciated'that the pressure of the liquidcouldbe maintained constant andth'e variationsrin; the.volume. .of discharge measured instead; In:either:case, the area of the outletsdefined bythe gauging member and the work surfaceaffects the flow of liquidin a-manner' susceptible; ot accurate measurement. Accordingly, theternr: flow. as used: herein'is' intended to apply-to. either: mode'of. operation.

I. claim; as myv invention:

1:.'.'Ahoning.tooli having; incombination; a rigid body: supporting. a circular series-of elongated abrasive. elements,- nozzle supporting members disposedon opposite sides of the tool bodyg'studs projectingfr'omrthe upper and'lower facesofsaid mem bers,;and .apair of yokesconn'ecting said studs "to; form a: rigid frame structure; saidtool body being recessed for the reception of said members whereby to guide the frame structure for movement radially of the tool body, and adjustable means carried by said members coacting with said tool'body to determine the position of said frame structure with respect to the tool body.

2. A honing tool having, in combination, a rigid body supporting a circular series of abrasive elements, nozzle supporting members disposed on opposite sides of th tool body, studs projecting from the upper and lower faces of the members, and yokes connecting said studs with the tool body, one of the studs associated with each of said members having a passage for conveying liquid to the nozzle supported by the member. I

3. A honing tool having, in combination, a rigid body supporting a circular series of'elongated abrasive elements, nozzle supporting members disposed on opposite sides of the tool body, studs projecting from the upper and lower faces of said members,.and a pair of yokes at opposite ends of said tool body, said studs being rigidly clamped to said yokes for supporting the members on the tool body.

4. A honing tool having, in combination, a rigid body supporting a circular series of elongated abrasive elements, nozzle supporting members disposed on opposite sides of the tool body, studs projecting from the upper and lower faces of said members, and a pair of okes connecting said studs to form a rigid frame structure, said tool body being recessed for the reception of said members whereby to guide the frame structure for movement radially of the tool body.

5. A honing tool having, in combination, a body, a plurality of abrasive elements supported on said body in a circular series, a pair of rigidly connected members mounted on said body for limited movement transversely of the axis of the body, said members adapted to coact with the surface of a cylindrical workpiece to define a pair of outlets located on opposite sides of the tool, spring pressed plungers mounted on said members adjacent the outlets adapted to engage with the work surface to center the outlets therein, and means limiting the movement of said plungers to interrupt their contact with the work surface as the workpiece approaches its finished dimensions.

6. A honing tool having, in combination, a body, a plurality of abrasive elements supported on said body in a circular series, a pair of members mounted on said body and rigidly connected together for limited movement transversely of the axis of the body, said members being adapted to coact with the surface of a cylindrical workpiece to define a pair of outlets located on opposite sides of the tool, and means operative automatically to center said members with reference to the workpiece.

7. A honing tool having, in combination, a rigid body, a plurality of elongated abrasive elements supported on said body in a circular series and movable radially thereof for engagement with the cylindrical surface of a workpiece, members mounted on said body for limited movement as 'a unit transversely of the axis of the body, said members :being adapted to coact with the surface of the workpiece to define a pair of outlets located on opposite sides of the tool and maintained substantially equal in effective area by the unitary movability of said members, and means connecting said outlets with a source of liquid under pressure.

8. In a honing tool in combination, a rigid body, a plurality of abrasive elements supported on said body in a circular series and movable radially thereof for engagement with a cylindrical work surface, a frame mounted on said body for movement transaxially of the body, a nozzle carried by said frame with its outlet disposed in close proximity to the work surface, means carried by said frame coacting with the work surface to center the frame within the work whereby to maintain uniform spacing of said nozzle from the Work surface while the tool is traversed through the work, and means connecting said nozzle with a source of fluid under pressure.

9. The combination with a rigid body adapted to be traversed axially through a cylindrical bore, of a plurality of nozzles spaced circumferentially around said body for coaction with the surface of the bore, and a frame supporting said nozzles in fixed spaced relation, said frame being mounted on said body for movement transaxially thereof to enable said nozzles to be centered in said bore irrespective of the position of the body therein, and means connecting said nozzles with a source of fluid under pressure.

10. The combination with a rigid body adapted to be traversed axially through a cylindrical bore, of a frame mounted on said body for movement transaxially thereof, a nozzle carried by said frame with its outlet disposed in close proximity to the walls of said bore, plurality of circumferentially spaced plungers mounted in said frame and yieldably urged into engagement with the walls of the bore to maintain said frame substantially centered therein independently of the position of said body, and means connecting said nozzle with a, source of fluid under pressure.

11. The method of gauging a cylindrical bore in process of being operated on by a honing tool which comprises, traversing a plurality of circumferentially spaced nozzles axially of the bore with a honing tool, discharging a constant volume of liquid coolant through said nozzles against the walls of said bore, measuring changes in the pressure of the liquid to detect changes in the restrictive action of the bore walls upon the discharge of the liquid from said nozzles, and maintaining said nozzles substantially centered in the :bore irrespective of the position of the honing tool therein.

JOSEPH O. OLSEN. 

